This invention relates to a system for providing quantification of two-dimensional image information, particularly, to an image quantifying method and apparatus that sets a reference value by which an image included within a region of interest that has been set on a two-dimensional digital image is tested for its significance.
Various detection methods have been known in the art. They include i) an autoradiographic detection method in which a living body administered a radiolabelled substance or a portion of a tissue of such living body is subjected to contact sensitization or exposure on a radiation film or the like for a specified time to obtain position information for the radiolabelled substance in the specimen, ii) a chemiluminescence detection method in which an immobilized polymer such as protein or nucleic acid sequence that has been selectively labelled with a chemiluminescence emitting marker is contacted by a chemiluminescent substance to produce chemiluminescence in the visible range, which is detected to give polymer-related information such as genetic information, iii) an electron microscopic detection method in which a metallic or non-metallic sample is exposed to electron beams and the resulting diffraction or transmission image of the sample is detected to perform its elemental, compositional or structural analysis, or a tissue of a living body is exposed to electron beams and the resulting image of the tissue is detected, and iv) a radiation diffraction image detection method in which a sample is irradiated and the resulting radiation diffraction image of the sample is detected to analyze its structure. In all of these methods, photographic films such as high-speed x-ray films are used as a detecting material, on which radiation image, chemiluminescent image, electron micrographic image, radiation diffraction image, etc. are recorded as visible image that can be detected with the human eye.
In these various detection methods, it was recently proposed that photographic films heretofore used as the detecting material should be replaced by a stimulable phosphor which, upon exposure to radiation, visible light, electron beams, etc., absorbs their energy in a cumulative manner and, when later excited with electromagnetic waves or exciting light in a specified wavelength range, emits stimulated light in a quantity proportional to the accumulated energy of the applied radiation, visible light or electron beams. The stimulated light from the phosphor is detected photoelectrically and converted to digital signal; the resulting image data is subjected to specified image processes to produce an image which is reproduced on a display device such as a CRT screen or a photographic image. The use of the stimulable phosphor eliminates the need to perform a chemical treatment called xe2x80x9cdevelopmentxe2x80x9d. The detection methods using the stimulable phosphor have other advantages including high speed which contributes to a considerably shorter exposure time and easy exposure, as well as good linearity between the energy of applied radiation, visible light and electron beams, and the resulting image intensity, plus great breadth of the linear range which means a wide dynamic range and high reliability in quantification. As a further advantage, the image intensity can be obtained as a digital image signal (data) and conversion to digital signal precedes image reproduction; therefore, by performing signal processing on the obtained digital image data, a desired image can be reproduced or quantitative analysis can: be accomplished with a computer.
Image forming and analyzing apparatus for use with an autoradiographic detection method, a chemiluminescence detection method, an electron micrographic detection method and a radiation diffracttion image detection method that share the common feature of using the stimulable phosphor sheet to generate image data and reproducing an image on the basis of the generated image data have been disclosed in commonly assigned Unexamined Published Japanese Patent Application (kokai) Nos. 334662/1995, 43538/1996 and 247931/1996. The disclosed image forming and analyzing apparatus are so adapted that in order to make comparison between desired regions of an image, a desired region of the image data is defined as a region of interest and the quantity of light emission from the stimulable phosphor sheet is digitized as the intensities (densities) of the image-creating pixels in this region of interest and the total sum of their intensities is determined for subsequent quantitative treatment; the apparatus are also adapted to be such that two or more regions of interest are grouped together and pertinent parameters such as the relative intensities of the regions of interest in the same group are calculated to enable subsequent quantitative analysis. To fulfill these functions of the apparatus, the region of interest in a displayed two-dimensional image as on a display device is delineated by a circle, a rectangle or a graphic figure bounded by kinked lines and graphic data such as coordinate data for these figures are stored as a separate entity from the image data, thereby enabling quantitative treatment or analysis of the intensities of the pixels in the region of interest.
The image data obtained by detection with the stimulable phosphor sheet contains not only various kinds of detected image data, it also contains diverse background noise. Noise components to be mentioned first are those which, during sensitization or exposure of the stimulable phosphor sheet, occur practically uniformly on the sheet due to cosmic rays and the radiations in the ground or the inherent radiation from the thin-layer chromatographic (TLC) plate for promoting development in TLC which is often practiced in studies of drug metabolism. Other noise components originate in the stimulable phosphor sheet when radiation image information is being read from it. In order to ensure more correct computing of intensity data for the individual pixels in the image that has been captured from the sheet, the data corresponding to the background which constitute the noise components must be removed from the intensity data for the individual pixels in the image.
To this end, the image forming and analyzing apparatus under consideration draws one or more graphic figures in that region of the displayed image which should inherently have a zero intensity and, using these xe2x80x9cbackgroundxe2x80x9d figures, calculates a reference background value (i.e., intensity per unit area) from their intensities. To determine the correct reference background value, the image analyzer disclosed in Unexamined Published Japanese Patent Application (kokai) No. 43538/1996, supra, adopts a special technique in which a plurality of background regions having figures of the same size and shape as a region of interest are set around the region of interest, the intensities of those background regions are determined, and a reference background value which is a threshold for evaluating the region of interest as a xe2x80x9csignificantxe2x80x9d one is determined from the statistical distribution characteristics of those intensities. For example, the intensities of those background regions are averaged to determine the xe2x80x9caverage intensityxe2x80x9d, which is used as the reference background value.
If the intensity of a single background figure is used as a reference background value, the correctness of the value is not guaranteed since it is largely dependent on the position where the background figure is set. This problem is absent from the image analyzer disclosed in Unexamined Published Japanese Patent Application (kokai) No. 43538/1996, supra; however, the method it adopts to solve the problem consists of setting a plurality of background regions having background figures of the same size and shape and determining the reference background value from the statistical distribution characteristics of their average intensity. Statistically, the obtained intensity data are deviated and unsuitable for insuring correctness in testing the region of interest for its significance. This problem is particularly great if the region of interest has low intensity.
The present invention has been accomplished under these circumstances and has as an object providing a method for image quantification by which even a region of interest having low intensity can be tested for its significance in a sufficiently rational and correct manner to realize correct quantitative treatment and analysis of the image in that region of interest.
Another object of the invention is to provide an apparatus for implementing the method.
In order to attain the object described above, the present invention provides an image quantifying method for performing quantification from two-dimensional digital image information, comprising the steps of setting a background region around a region of interest to be quantified in a two-dimensional image based on the two-dimensional digital image information, the background region not including the region of interest, determining a statistical distribution of pixel-based intensity for all pixels in the background region, determining an average intensity of the region of interest from a statistical quantity obtained from the statistical distribution, the average intensity serving as a reference for finding the region of interest significant, and testing the region of interest for its significance based on the determined reference average intensity.
It is preferred that the reference average intensity is expressed using a representative value of the statistical distribution which is selected from among statistical quantities of the statistical distribution and wherein the statistical distribution is an intensity histogram for the pixels in the background region.
It is also preferred that the histogram is smoothed for determining the representative value.
It is further preferred that the representative value is an average of the statistical distribution, which is also the reference average intensity.
It is yet further preferred that the representative value comprises an average A and a standard deviation S of the statistical distribution and wherein the reference average intensity is A+kS (where k is a positive number of 0-5).
It is still further preferred that the representative value comprises a mode M and a standard deviation S of the statistical distribution and wherein the reference average intensity is M+kS (where k is a positive number of 0-5).
In order to attain the another object described above, the present invention provides an image quantifying apparatus for performing quantification from two-dimensional digital image information, comprising a display device which displays a two-dimensional image based on the two-dimensional digital image information, a setting device which sets a background region around a region of interest to be quantified in the displayed two-dimensional image, the background region not including the region of interest, a statistical treatment device which determines a statistical distribution of pixel-based intensity for all pixels in the background region and determines a statistical quantity from the statistical distribution, a determining device which determines an average intensity of the region of interest from the determined statistical quantity, the average intensity serving as a reference for finding the region of interest significant, and a testing device which tests the region of interest for its significance based on the determined reference average intensity.
It is preferred that the determining device determines the reference average intensity using a representative value of the statistical distribution which is selected from among statistical quantities of the statistical distribution and wherein the statistical treatment device determines an intensity histogram for the pixels in the background region as the statistical distribution.
It is also preferred that the statistical treatment device smoothes the histogram for determining the representative value.
It is further preferred that the determining device selects an average of the statistical distribution as the representative value and wherein this average is substituted for the reference average intensity.
It is yet further preferred that the determining device selects an average A and a standard deviation S of the statistical distribution as the representative value and determines the reference average intensity as A+kS (where k is a positive number of 0-5).
It is still further preferred that the determining device selects a mode M of the statistical distribution and a deviation S from M as the representative value and determines the reference average intensity as M+kS (where k is a positive number of 0-5).